Sources state the product, set to compete against 800-lb. gorilla PayPal (EBAY-2.4%), will "allow online shoppers to make purchases on mobile apps using their Facebook login information," and (like PayPal) will allow them to avoid having to constantly re-enter their billing info.

However, for now, the test is focused on simply "creating a better mobile checkout experience," and doesn't tie in payment-processing (as PayPal does).

Facebook already handles payments for in-app game purchases and its Gifts product (among other things), and the enormous reach of its social sharing tools could allow it to quickly reel in many 3rd-party apps and (if it chooses to expand further) Web sites.

But PayPal has stared down competition from Internet giants before, and the network effects stemming from its 132M active users and many thousands of merchant partners make it a tough company to seriously disrupt. PayPal expects to handle $20B in mobile transactions this year, up from $14B last year.